When cells cultured in a culture vessel are collected, the cells adhering to the bottom of the culture vessel have to be peeled using a peeling agent such as trypsin. In order to recognize the peeled state of the cells at this time, a cell peeling recognizing method is used in which cells in the culture vessel to which the peeling agent has been added are imaged and the peeled state of the cells in the culture vessel is recognized on the basis of captured imaging data.
In Patent Document 1, a phase-contrast microscope is used to clarify the distinction between cells and the background in the imaging data. Because the brightness is increased when the phase difference of the peripheral portion of cells is increased by cell peeling, peeled cells are identified when the bright component exceeds a predetermined threshold value.
In Patent Document 2, because the area of the cells adhering to the culture vessel is decreased by peeling of the peripheral portion of cells previously adhering to the bottom of the culture vessel, peeled cells are identified when the area of the portion of the cells adhering to the bottom of the culture vessel is determined from captured images of the cells in the imaging data and the area has fallen below a predetermined threshold value.